This invention relates to well pipe hangers, and more particularly to concentric tubing hangers for use in wells requiring positive lock down of the hanger and control of the well annulus below the hanger.
General safety and operational requirements for oilfield tubing and casing hangers impose several constraints on the design of the hangers, the wellheads and the other well components with which the hangers cooperate. Some of the more important features of these hangers comprise sealing devices at various locations, such as between the hanger and the wellheads and/or the Christmas tree, and within the hanger bores themselves, to isolate pressure below the hanger; a positive locking device to prevent accidental release of the hanger from the wellhead, such as due to trapped pressure below the hanger or thermal expansion of well tubulars; and conduit(s) through or around the hanger for control of the well production/injection annulus below the hanger. Earlier hangers, specifically tubing hangers, were not required to effect metal seals between the interfacing components primarily due to the fact that accepted technology in this area did not exist, but metal seals are now commonly specified by operators. Although some hangers with metal elements for providing access to or isolation of the annulus, such as sliding sleeves or poppet rings, are known, the sealing components in those designs are totally resilient in nature and, therefore, do not satisfy specifications calling for metal-to-metal sealing at that location.